Recently, according to the Chinese Academy of Sciences, the team of Liu Jinchuan, a foreign academician of the Chinese Academy of Engineering and a professor at the City University of Hong Kong, creatively proposed a 3D printing strategy to develop high-strength, high-plasticity titanium by regulating the mixing degree of different powders in the molten pool. alloy. Related research results were published in "Science" a few days ago.
Generally speaking, the inhomogeneity of composition in metal materials is often regarded as a major defect, which researchers have been trying to avoid. On the one hand, people lack sufficient understanding of the positive effects of compositional inhomogeneity; on the other hand, traditional methods are usually unable to effectively control the compositional fluctuations in materials.
Through previous computational simulation studies, the researchers found that a certain degree of compositional inhomogeneity helps to create a unique heterogeneous microstructure, thereby improving the mechanical properties of the material. Therefore, they believe that the non-uniformity of the material composition can be actively used and become an effective alloy design method.
In order to control the composition fluctuations inside the alloy, the researchers used 3D printing technology. This is a simple direct forming technique, but few people think of applying it to alloy design. During the 3D printing process, the metal powder will melt and solidify rapidly. Due to the ultra-fast cooling rate, the composition gradient generated in the molten pool is successfully retained.
Liu Jinchuan and some team members (Photo courtesy of City University of Hong Kong)
Based on this new idea, researchers tried to mix and print two common alloy powders (including stainless steel powder) in the 3D printing process. Through carefully selected powder types and special printing parameters, they achieved a controllable micron-level composition gradient.
Liu Jinchuan said that this micron-level composition gradient not only brings phase stability and spatial modulation of the microstructure but also improves the mechanical properties of titanium alloys, making it the smallest grain size that can be achieved in 3D printing titanium alloys. One of the sizes.
Liu Jinchuan also said that this is a metastable titanium alloy with a lava-like microstructure. "This unique microstructure brings excellent mechanical properties and fine grain structure to the alloy, enabling the alloy to have ultra-high-strength while still having extremely high uniform deformability and maintaining the low density of titanium alloys."
